Use a separate mutex for BLASTBufferQueue in BLASTBufferItemConsumer am: 5c8b18c908 am: a3970b8d21 am: 5f8970b4bc

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/15728802

Change-Id: I81d6f97dc79b3a30d1bc2cea7220d5bcc5833788